Power factor Correction (PFC) may be defined as the ratio of real power to apparent power, and expressed as: power factor (PF)=Real Power/Apparent Power, where Real Power is expressed in Watts, while Apparent Power is expressed in volt-amperes (VA). In this expression, the real power is determined as the average of the instantaneous product of current and voltage across a phase or cycle, while the apparent power is deemed as the RMS value of current times the voltage. This suggests that when current and voltage counterparts are sinusoidal and in phase with each other, the resultant power factor is 1.0 which is deemed to be the ideal condition. A switch mode power supply (SMPS) is often used to efficiently convert an alternating current (AC) input voltage to a direct current (DC) output voltage. In many cases, power factor is a desirable parameter to control in SMPS design in order to provide power as efficiently as possible.